The present invention relates to real time sensing of subsurface geological conditions. In particular, the present invention relates to an advantageous apparatus and method for sensing the physical conditions present in a geologic formation during the in situ processing of hydrocarbons.
As the world's standard crude oil reserves are depleted, and the continued demand for oil causes oil prices to rise, oil producers are attempting to process hydrocarbons from bituminous ore, oil sands, tar sands, and heavy oil deposits. These materials are often found in naturally occurring mixtures of sand or clay. Because of the extremely high viscosity of bituminous ore, oil sands, oil shale, tar sands, and heavy oil, the drilling and refinement methods used in extracting standard crude oil are typically not available. Therefore, recovery of oil from these deposits requires heating to separate hydrocarbons from other geologic materials and to maintain hydrocarbons at temperatures at which they will flow. Steam is typically used to provide this heat, although electric and radio frequency heating is sometimes employed. The heating and processing can take place in-situ, or in another location after strip mining the deposits.
During in-situ processing, it is extremely difficult to sense in real time the conditions in the deposit and/or the well bore. There is often uncertainty regarding the stage of the process, e.g., whether the hydrocarbons are indeed flowing. Valuable time and heat energy are wasted in unsuccessful attempts at in-situ processing when low formation permeability conditions prevent diffusion of steam and limit heating, or when steam and heat moves away from a zone that is targeted for heating through formation fractures or through high permeability materials.
Electrical transmission lines are commonly used for conveying radio frequency (RF) energy from one location to another. Such lines include shielded and unshielded types, e.g. coaxial cable and open wire types respectively. As unshielded transmission lines are open to surroundings, they can transduce electromagnetic fields into the media in which they are immersed. Thus, there may be a need for a low frequency electromagnetic transducer, such as an antenna that can penetrate dissipative media.
Conventional electromechanical “well logging” is presently used to monitor and record subsurface conditions. Well logging typically involves an examination of core samples, and moving sensors up or down the well bores. Sensors are used to measure, for example, electrical resistance, acoustic properties, natural radioactivity and density of the formation surrounding the well. However, these measurements do not produce a real-time, overall picture of conditions in the formation. They disclose only a static and partial picture of the conditions in the formation.